Scanning electron microscopy and molecular dynamics of surfaces of growing and ablating hexagonal ice crystals

• Main Authors: W. C. Pfalzgraff, R. M. Hulscher, S. P. Neshyba
• Format: Article
• Language: English
• Published: Copernicus Publications 2010-03-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/10/2927/2010/acp-10-2927-2010.pdf

We present the first clearly resolved observations of surfaces of growing and ablating hexagonal ice crystals using variable-pressure scanning electron microscopy. The ice surface develops trans-prismatic strands, separated from one another by distances of 5–10 μm. The strands are present at a wide range of supersaturations, but are most pronounced at temperatures near the frost point. Pyramidal facets consistent with Miller-Bravais indices of 10<span style="border-top: 1px solid #000; color: #000;">1</span>1, and possibly also 20<span style="border-top: 1px solid #000; color: #000;">2</span>1, are associated with ice growth under these conditions. A molecular-dynamics model of a free-standing ice <i>I</i><sub>h</sub> nanocolumn containing 8400 water molecules does not develop trans-prismatic strands, suggesting these features originate at larger spatial or temporal scales. The possible relevance of these surface features to cirrus ice is discussed.